Island



'(No Model.) v

L. W. DOWNBS. GUT-OUT FOR BLECTRIQ CIRCUITS.

No. 569,373. Patented Oct. 13, 1896 With/asses. 1767167020). y W 7/. W aza'zw W I I 7 UNITED STATES PATENT EEicE.

LOUIS IV. DOIVNES, OF PROVIDENCE, RI-IODE ISLAND, ASSIGNOR OF ONE- I'IALF TO IVILLIAM C. \VOODW'ARD, OF SAME PLACE.

CUT-OUT FOR ELECTRIC CIRCUITS.

SPECIFICATION forming part of Letters Patent No. 569,373, dated October 13, 1896.

Application filed July 23,1896. Serial No. 600,298. (No model.)

To all whom it may cancer-w:

Be it known that I, LOUIS W. DOWNEs, of Providence, Rhode Island, have invented a new and useful Improvement in Cut-Outs for Electric Circuits, which improvement is fully set fort-h in the following specification.

This invention has reference to the construction of fusible cut-outs adapted to be included in electric circuits for the protection of the instruments therein from the destructive action of high-potential currents.

In my United States Patent No. 561,159, dated June 2, 1896, I have described a cutout in which the fuse wire or strip is inelosed in a tubular sheath confining a body of air and provided with contracted ends capable of expanding when the fuse is ruptured and permitting the rapid escape of the heated air. In order to render such a fuse more efficient and certain in action and particularly to pre vent the formation and continuance of an arc, it has been proposed to surround the f use-wire with a fin ely-divided an d refractory material-such as fine sand, powdered marble, plaster-of-paris, and powdered pumice in a loose condition. Extensive experiments with such a fuse, however, have shown it to be defective. The main difficulty encountered was that the melting-point of a fuse thus completely surrounded with the insulating material changed rapidly with the length of time it was in circuit. For example, I have found that a fuse which would melt in three seconds at forty-eight amperes would after thirteen minutes melt at thirty amperes. This is of course due to the gradual absorption of heat by the surrounding material, which conducts less rapidly when hot than when cold. In proof of this I found that when the temperature at the surface of the tube was not more than 50 oentigrade the temper ature at the fuse itself was about 150 centigrade. Increasing the radiatingsurface had little or no effect, and if the current was reduced to a value that it would carry continuously the difference between this current and the melting-current was too great, so that the fuse afforded little or no protection for overload, but only for cases of short circuit.

The objects of the present invention are to overcome the difficulties above referred to and to produce a fuse much superior in point of efficieney, certainty of action, and in the prevention of the formation and continuance of an arc than those heretofore known. These objects I have effectually accomplished by surrounding a portion of the fuse-wire by a body or layer of air, which is itself surrounded by the finely-divided insulating material inclosed within an outer sheath. To provide such an air-space, I inelose a portion of the fuse-wire within a hollow cylinder or drum, preferably made of paper and having perforations therein for the escape of gas. The drum may or may not be of the same diameter as the bore of the inclosing sheath, which is preferably a mica tube closed at its ends by perforated brass caps fitting closely about the conductor. The space within the exterior sheath and about the drum inclosing the air-space is filled by a finely-divided material, the office of which, in a properly-constructed cut-out, is to provide a multitude of minute paths for the escape of the vapor or gases produced at the rupture of the circuit, preventing the formation of a continuous strata of the same, which from the fact that it possesses a fairly good conductivity would maintain an arc. Upon the rupture of the circuit an arc is of course formed within the drum, and it has been found that if the surrounding material possesses silica enough the heat of the arc causes a combination between the vaporized metal and the silica, resulting in the formation of a species of slag or glass at the ends of the drum in the shape of what might be called stoppers or buttons, that prevent the necessary escape of gas. In this manner the arc would be maintained until the tube was destroyed. It is therefore apparent that the filling should be of a material as free as possible from silica or other substance which, under the heat of an arc, would form a slag or glass, either by combination or not, producing any solid mass which would prevent the escape of gas. I have used for this purpose with success slaked lime, and although this is preferred any other suitable material may be employed. In a cut-out so constructed the poor heat-conducting properties of the layer of surrounding air prevents the too rapid dissipating of heat, and thus brings the melting-current Within reasonable range of the continuous load-current and also prevents any material change in the melting-current value due to absorption of heat by the surrounding mass.

In the accompanying drawings, illustrating a cutout embodying the features of the present invention, Figure 1 is a longitudinal section, and Fig. 2 is a perspective View showing the drum inelosin g the air-space in place upon the fuse-wire.

The protective sheath is preferably formed of a mica tube a, having perforated brass caps or end pieces a, fittingat their extremities closely about fuse-Wire Z); but the im provements constituting the present invention. may obviously be applied to tubes of different forms and materials.

0 is the perforated drum partly inclosing the fuse-wire and forming an air-space about the same.

(Z is the finely-divided refractory material loosely filling the sheath about the drum 0.

I have not shown in the drawings the mounting of the fuse, as this may be of any suitable description and forms no part of the invention.

Modifications may be made Without departing from the nature and principle of the invention.

Having thus described my invention, what I claim as new and desire to secu re by I ,etiers Patent, is-

1. In a safetycut-out, a fuse-wire combined with an inciosing sheath, and surrounded by a mass of finely-divided refractory material in a loose condition, placed in said sheath in such manner as to leave an air-space about the fuse-Wire, substantially as described.

2. In a safety cut-out, the combination with a fuse-Wire, of an inclosing sheath, a pcrft rated drum Within said sheath partially inclosing the fuse-wire to form an air-space about the same, and a mass of linely-divided refractory material-such as slaked limefilling the sheath about said drum, substantially as described.

In a safety cut-out, the combination with a fuse-wire, of an. inelosing sheath consistin of a tube with perforated end pieces or caps, a perforated paper drum within said sheath, partially inclosing the fuse-Wire to form an air-space about the same, and a mass of finely-divided refractory 1naterialsuch as slaked 1in1efilling the sheath about said drum, substantially as described.

I11 testimony whereof I have signed this specification in the presence of two subscribing witnesses.-

Witnesses:

JOHN HnNsHAW, JAMES IT. THU iS'IOX. 

